Double dry-running gas barrier seal arrangements are currently known and are utilized in various industrial applications, particularly chemical and petrochemical applications, so as to reduce the level of emissions leakage. In the typical double gas barrier seal arrangement, inner and outer mechanical seal assemblies are positioned in axially spaced relationship relative to a rotatable shaft, such as a pump shaft, with the seal assemblies coacting between the shaft and the surrounding housing to create a seal between opposed relatively rotatable annular seal faces as defined on the rotor and stator of the respective seal assemblies. An inert gas, such as air or nitrogen, is typically supplied into a barrier chamber defined between the two seal assemblies, with the barrier gas typically being at a pressure greater than the product pressure, to prevent product leakage. Any leakage across the inner seal assembly thus results in the gas entering the product, and any leakage across the outer seal assembly results in acceptable emission of air or nitrogen into the environment.
In one known double seal arrangement of the type explained above, specifically an arrangement manufactured by John Crane, the inner and outer seal assemblies are provided with spiral groove patterns provided on the rotors of both seal assemblies. The groove pattern is exposed to the barrier gas and functions to pump the barrier gas toward the ungrooved portion of the seal face so that a compressed gas cushion is formed which serves as a sealing dam to prevent escape of product being sealed. By providing a grooved seal face which receives barrier gas therein, this is also believed to reduce face contact pressure and hence reduce face heat generation and friction.
Another known seal assembly which provides a grooved face exposed to a barrier gas is manufactured by Borg-Warner, and includes radially directed deep grooves which at one end communicate with the barrier gas and at the other end communicate with a small annular groove, the latter in turn surrounding a nongrooved annular portion of the seal face which functions as a barrier or dam.
While seal assemblies of the type described above utilizing both spiral grooves and radial grooves have been known and utilized for a significant period of time, and while these seal assemblies are effective for minimizing product leakage while at the same time reducing frictional contact pressures between the seal faces and hence minimizing frictional forces, heat generation and face wear, nevertheless it is believed that these operating conditions can be still further improved by improving the configuration of the groove pattern formed on the seal face.
For example, it is desired to provide an improved deep groove pattern which is effective for maximizing the supply of barrier gas into the grooves for deposition between the opposed seal faces to minimize the contact pressure and hence reduce friction and wear and temperature, and at the same time provide a groove pattern which can effectively accomplish this function irrespective of seal ring rotation, namely by providing an improved groove pattern which is effectively bi-directional. While the groove pattern of the Borg-Warner seal described above is bi-directional, nevertheless the radial orientation of the grooves prevents them from creating any significant pumping effect with respect to forcing gas into the grooves, and the radial grooves are effective only for low pressure differentials between the product (or environment) and barrier gas. While the spiral grooves of the John Crane seal do provide a pumping effect in one rotational direction, they are highly ineffective in the other rotational direction. Also, these spiral grooves are typically shallow and hence operate on a different principle, namely on a hydrodynamic layer which is effective only at higher rotational speeds.
Accordingly, it is an object of this invention to provide an improved mechanical seal assembly having a deep groove pattern on the rotating seal face, which groove pattern communicates with a barrier gas to provide a highly improved degree of performance, particularly improved performance at high differential pressures and in either rotational direction, and which overcomes and improves upon the performance of prior seal assemblies of this general type.
More specifically, this invention relates to an improved mechanical seal assembly having a deep groove pattern formed in the face of the rotating seal ring, which groove pattern includes two sets of straight angled grooves, one set being angled in one rotational direction,the other set being angled in the opposite rotational direction, to provide effective pumping of barrier gas into the grooves irrespective of the direction of rotation, and to provide improved hydrostatic performance to reduce contact pressure between the seal faces even at high pressure differentials between the product/environment and barrier gas.
In the improved seal assembly of this invention, the groove pattern preferably also includes a deep annular groove which is formed in the seal face and communicates with the radially inner ends of the angled grooves to facilitate flow of barrier gas into and through the grooves to greatly improve the cooling of the seal faces and the minimization of contact pressure between the seal faces. This overall groove pattern also results in formation of several face pads which are disposed in series along the dam, with each pad being defined circumferentially between two angled grooves and radially outwardly of the annular groove. These pads act as bearing supports to reduce the overall unit loading between the seal faces, and also develop a slight lift due to thermal waviness so as to reduce unit loading across the seal faces. The overall groove pattern, and specifically the manner in which the angled grooves communicate with the annular groove, facilitate the removal of wear debris from between the seal faces. In addition, the angled grooves force the barrier gas down into the annular groove, irrespective of the direction of rotation, which annular groove creates a hydrostatic pressure dam in complete surrounding relationship to the seal face dam so as to minimize contact pressure or unit load on the face dam, and at the same time prevent leakage of product across the face dam due to the pressure of the barrier gas being higher.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.